Refining of lubricating oils



2,779,711 Patented den. 29, 1957 lice 2,779,711 REFINING F LUBRICATINGOILS Louis A. Goretta, Hammond, Ind., assignor to Standard Gil Company,Chicago, Ill., a corporation of Indiana No Drawing. Application February7&8, 1955, Serial No. 491,199

4 Claims, (Cl. 196-24) This invention relates to improvements inlubricating oil refining and more particularly provides a process fortreating raw distillate lubricating oil stocks in the presence ofhydrogen and a catalyst.

Conventional lubricating oil refining requires one or more extractionoperations with acid or a selective solvent usually followed by claytreating in addition to the standard distillation and dewaxing ordeasphalting operations. The availability of cheap by-product hydrogenfrom catalystic reforming plants has created a great deal of interest inthe use of hydrogen treating processes, so called hydrofinishingprocesses, as an alternative to conventional extraction and claytreating. Treatment of lubricating oil stocks under mild conditions ofhydrogenation improves color, viscosity index, and in generalcontributes to the stability of the oil. In practice however, it hasbeen found necessary to operate on partially refined stocks, i. e.lubricating oil distillates which have been first extracted with acid ora solvent and preferably have been treated for removal of wax, in orderto avoid costly stock losses while attaining the desired improvement incolor and stability. Thus, in the present state of the art,hydrogenation of lubricating oil stocks is in general limited tofinishing operations without eliminating expensive acid treating and/ orsolvent extraction. When unextracted or raw stocks are subjected tohydrogenation, the severity of treatment required with conventionallyavailable catalysts results in excessive production of light ends whichmust be separated from the treated product to meet flash and viscosityspecifications.

A particular problem with raw feeds is color instability of the treatedoils. Although a satisfactory initial color is obtained, meetingspecifications, there is excessive degradation in color quality uponstorage. For example, where a conventionally refined oil of 1.5 to 2.5NPA color (ASTIvl-D155-45T) may darken upon aging at 100 C. for 24 hoursto 2.0 to 3.0, a hydrogenated oil may darken to 3.0 to 3.5 or 4.5 or 5.0NPA. It is undesirable to have the color darken more than /2 NPA uponaging.

I have discovered that a raw distillate lubricating oil stock can beeconomically processed to a stable product under selective conditions byuse of an alkalized hydrogenation catalyst. The most suitable catalystis alkalized cobalt oxide-molybdenum oxide-alumina, but alkalizedmolybdenum oxide-on-alumina' and alkalized chromium oxide-on-aluminaalso appear to have value. Other Wellknown hydrogenation catalysts,however, such as platinum-on-alumina and tungsten-nickel sulfide appearto be distinctly marginal. Surprisingly, the alkalized molybdenum andchromium oxide type hydrogenation catalysts do not appear to afford anysignificant advantage in processing extracted or partially refinedlubricating oil stocks. But in processing Waxy or unextractedlubricating oil stocks, the alkalized catalysts of the invention producelight colored oils of satisfactory color specification and stabilitywhere the less selective corresponding unalkalized catalysts do not.Moreover, the production of light ends in the hydrogenation process issubstantially reduced, by from about 25 to upwards of 50 percent,resulting in substantial savings of valuable lubricating oil stock.

In the practice of the invention, the feed is a raw distillatelubricating oil stock having a viscosity which may range up to that ofthe SAE-40 range. Advantageously, however, the invention is applied tostocks in the viscosity range of SAE 10 and 20 oils. The feed stock isnot treated by preliminary extraction with acid or solvent andadvantageously is a waxy distillate, i. e. has not been subjected to apreliminary dewaxing operation. The preheated stock together withhydrogen is passed in contact with a bed of particle form hydrogenationcatalyst, e. g. a cobalt oxide-molybdenum oxide-alumina catalyst whichhas been alkalized by incorporation of an oxide or salt of an alkalimetal or alkaline earth metal, e. g. 4 percent potassium oxide. Thecatalyst is disposed in the form of a fixed bed of pellets, pills orbeads, and the feed is passed, advantageously down-flow, through thecatalyst bed. A temperature in the range of about 650 to 850 F.,preferably about 800 to 825 F., and a pressure of about 500 to 2500 p.s. i. g., preferably about 11000 to 1500, are maintained. The spacevelocity may be varied in the range of about 0.5 to 10 L. H. S. V.,controlling the severity of treatment. The hydrogen rate is in the rangeof about 1,000 to 6,000 cubic feet per barrel although hydrogenconsumption is low and ordinarily should not exceed about 200 to 400cubic feet per barrel. After the feed has been subject to contact withthe catalyst under the above hydrogenation conditions, unreactedhydrogen is separated. The unreacted hydrogen may berecycled or may bediverted to other purposes such as refinery fuel depending upon thedesign of the facilities. The treated oil is steam or vacuum stripped toremove light ends formed in the process.

The process of the invention permits the processing of raw waxy stocksdirectly without preliminary dewaxing and solvent extraction.Specification products may be obtained by selective treating atseverities low enough to minimize stock losses, thus protecting theeconomic gains made by quality improvement and elimination ofconventional acid and/or solvent refining methods. Processing waxystocks provides a further advantage in improving the yield and qualityof parafiin waxes produced by subsequent dewaxing operations.

The catalysts used with the process of the invention are convenientlyany of the conventionally available chromium oxide-alumina, molybdenumoxide-alumina and cobalt oxide-molybdenum oxide-alumina hydrogenationand reforming catalysts, after selective promotion with an alkalinesubstance. A particularly suitable alkali is potassium hydroxide, butother alkali metals such as sodium and lithium, for example, may beemployed, advantageously in the form of their oxides or hydroxides, butalso in the form of other Water soluble salts such as borates, nitrates,carbonates, bicarbonates, acetates, sulfates, phosphates and the like.An example of the last named which is particularly suitable is disodiumhydrogen phosphate. Oxides and salts of the alkaline earth metals alsohave values, for example calcium oxide or calcium bicarbonate.

The simplest method for incorporation of the alkali promoter is byimpregnation with an aqueous solution of the soluble alkali in thedesired concentration. The catalyst is then dried and calcined at anelevated temperature, e. g. 800 to 1200 F., for use. Alternatively, thealkali promoter may be incorporated in the catalyst composition at anydesired stage in its preparation before drying and calcining. Theconcentration of alkaline promoter may be in the range of 0.5 to about10 mol percent, but there is an optimum concentration of alkali promoterfor each catalyst composition for color stabilization and minimum stocklosses. Sincethe optimum concentration depends upon the nature ofthefeed stock and correlation with process conditionsin addition to.catalyst composition; it

is necessary to resort to screening tests to determine the best catalystcomposition for a given operation. In gen: eral, a concentration ofabout 2 to 4 mol percent of alkali promoter appears to give the bestresults, particularly with potassium.

The starting hydrogenation catalysts may be made by several methods. Forexample, alumina either in the form of a synthetic alumina gel or anactivated alumina or bauxite can be impregnated with an aqueous solutionof a salt of the metal giving the desired active oxide upon drying andcalcination. Also the catalyst can be prepared by err-precipitation ofthe alumina base material with the molybdenum oxide or chromium oxidefrom a mixture of :aqueous solutions of corresponding salts. Theresulting composites are dried, extruded or pelleted, and calcined. Thecobalt oxide-molybdenum oxide-alumina catalyst, which represents apreferred form of catalyst for practicing the invention, may be preparedby impregnating a molybdenum oxide-alumina catalyst, or the catalyst maybe prepared by co-precipitation from a mixed aqueous solution of solublesalts. The concentration of metal oxides may be varied quite widely inthe finished catalyst although in the case of the molybdenum oxidecatalysts, the concentration of molybdenum oxide ordinarily will be lessthan about mol percent. The proportion of cobalt also may vary butusually will be in the range of about 1 mol percent to 6 mol percent. Itmay be in the molecular proportions for formation of cobalt molybdate inthe co-precipitated type catalyst if desired. The following examplesillustrate specific aspects of the invention.

EXAMPLE I The catalyst was prepared by dissolving 22 grams of potassiumnitrate in 85 cc. of water and impregnating 200 grams of a commerciallyavailable (Oronite) cobalt oxide-molybdenum oxide-alumina catalyst withthe resulting solution. The catalyst contained 3.6 percent C00, 11.2percent M003 and 4 percent K20. The catalyst was dried and calcined at1000 F. for one hour.

An SAE-10 parafiin distillate from a pipe still running Mid-Continentcrude oil Was used as the feed stock. The feed had an initial NPA colorof 2.5; after aging for 24 hours at 100 C., the NPA color was 4.5. Thefeed was passed with hydrogen at a rate of 2810 set/barrel over a bed of6 to 14 mesh catalyst pellets. The reaction conditions were controlledat a temperature of 800 E, a pressure of 1000 p. s. i. g. and a spacevelocity of 5.27 L. H; S; V. The reactor efiluent was vacuumed strippedto a pot temperature of 400 F. at 2 to 2 /2 mm. The treated oil had aninitial color of 1.6 NPA and an aged color of 2.4.

The light ends off the treated oil, constituting 2.73 percent of thefeed, turned dark on standing at room temperature for only a few hours.Similar discoloration of light ends produced by treating with aconventional cobalt oxide-molybdenum oxide-alumina catalyst or anickeltungsten sulfide catalyst has not been observed. Hence, the colorforming bodies responsible for instability appear to have beenpreferentially attacked by the alkalized catalyst and eliminated withthe light ends.

By comparison, treatment with unalkalized, or conventional, cobaltoxide-"molybdenum oxide-alumina catalyst is less eifective in colorimprovement under similar conditions and, with respect to colorstabilization, is exceedingly unreliable. Also the production of lightends is considerably higher, being in the range of 9 to 13.5 percentunder the comparable conditions.

EXAMPLE II In the first series of runs, an SAE-10 waxy distillate waspassed over a bed of the pelleted catalysts at a temperature of 800 F.,a pressure of 1000 p. s. i. g. of hydrogen and a space velocity of 5 L.H. S. V. in the second series of runs. an SAE-ZO unextracted distillateWas treated under the same conditions with a 4 percent K20 on thechromia-alumina catalyst. The results of the two series of runs aretabulated below in Tables 1 and 2.

Table I NPA Color Percent K20 in Catalyst Initial Aged Table II NPAColor Initial i Aged Feed 2. 3 7. 5 Product 2. o l 3. 7 J) i4.. n#

EXAMPLE III A disodium phosphate-cobalt oxide-molybdenum oxidealurninacatalyst containing 4 mol percent C00, 6 mol percent M003, 5 mol percentNAZHPQ; and mol percent alumina was prepared by co-preeipitating anaqueous solution of mixed salts of cobalt, molybdenum and aluminum withdisodium phosphate, drying and calcining. An unextracted SAE-lOparafifin distillate having an initial NPA color of 2.8 and an agedcolor of 8 NPA was treated over the catalyst at 800 E, 1000 p. s. i. g.,5+ 1.. H. S. V. and 3000 cubic feet of hydrogen per barrel. The treatedproduct had an initial NPA color of 1.7 and an aged NPA color of 2.7.Approximately 7 percent light ends were separated when the product wasstripped to the initial flash point of the feed before the colordeterminations.

I claim:

1. A process for producing color stable lubricating oil by hydrogenatingan unrefined distillate lubricating oil stock derived from a mixed-basecrude oil which is characterized by color instability which processcomprises contacting the stock with cobalt oxide-molybdenum oxidealuminahydrogenation catalyst which has been alkalized by incorporation ofabout 0.5 to 10 mol percent of an alkali selected from the groupconsisting of compounds of alkali metals and alkaline earth metals, inthe presence of hydrogen at a temperature in the range of about 650 to850 F., :a pressure in the range of about 500 to 2500 p. s. i. g. and aspace velocity in the range ofv about 0.5 to 10 W. H. S. V.

2. The process of claim 1 in which the catalyst is alkalized byincorporation of about 2 to 4 mol percent of potassium oxide.

3. The process of claim 1 in which the catalyst is stabilized byincorporation of about 2 to 4 mol percent disodium phosphate.

4. The process of claim 1 in which the unrefined distillate lubricatingoil stock is in the viscosity range of about SAEl0 and SAE-ZO oils.

References Cited in the file of this patent UNITED STATES PATENTS2,441,297 Stirton May 11, 1948 2,442,372 Smith et al. June 17, 19472,608,521 Hoog Aug. 26, 1952 2,697,064 Brown Dec. 14, 1954 2,697,683Engel et al. Dec. 31, 1954 OTHER. REFERENCES Jones: The Oil and GasJournal, Nov. 1, 1954.

1. A PROCESS FOR PRODUCING COLOR STABLE LUBRICATING OIL BY HYDROGENATINGAN UNREFINED DISTILLATE LUBRICATING OIL STOCK DERIVED FROM A MIXED-BASECRUDE OIL WHICH IS CHARACTERIZED BY COLOR INSTABILITY WHICH PROCESSCOMRISES CONTACTING THE STOCK WITH COBALT OXIDE-MOLYBDENUM OXIDEALUMINAHYDROGENATION CATALYST WHICH HAS BEEN ALKALIZED BY INCORPORATION OFABOUT 0.5 TO 1 0 MOL PERCENT OF AN ALKALI SELECTED FROM THE GROUPCONSISTING OF COMPOUNDS OF ALKALI METALS AND ALKALINE EARTH METALS, INTHE PRESENCE OF HYDROGEN AT A TEMPERATURE IN THE RANGE OF ABOUT 650* TO850* F., A PRESSURE IN THE RANGE OF ABOUT 500 TO 2500 P.S.I.G. AND ASPACE VELOCITY IN THE RANGE FO ABOUT 0.5 TO 10 W.H.S.V.